Disclaimer: Believe it or not I'm walking on air. I never thought I could fly so high. Believe it or not I don't own any of these characters, however.
"So, let me get this straight..." The Dark Knight's voice was as flat and emotionless as it would be on a criminal investigation. Which was how it appeared to his younger cohorts he was treating this. He started in front of his youngest partner, Robin, who was in costume, sans mask. The beginnings of what looked to be an impressive shiner was forming around his right eye. "You decided to play a prank on Nightwing."
Tim exclaimed, "He started it! He put knockout gas in my-"
"YOU!" Batman interrupted in a roar, glaring down at him, "Decided to play a prank on Nightwing. Establishing your motive hardly helps your case." Tim was silent as Batman glowered at him. "So you put dye in the shampoo in the guest bathroom, knowing he was staying there." He moved onto Batgirl.
Like Tim, Cassandra was in her costume, but without the cape and cowl. She scowled at Tim, her now-blond hair pulled back and bound behind her head. "He started it." she said.
Batman ignored that entirely. "You," he continued, "used the shampoo and then went down to the cave." Batman paused, "When did you put your costume on?"
"Only clothes," Cass answered. She wasn't a regular visitor to the upstairs portion of the Manor, and her identity, such as it was, had no connection to Bruce Wayne. No clothes of hers would be kept there.
Batman nodded, "We'll get to your violating the 'no costumes upstairs' rule in a minute." Her shoulders slumped and he continued, "So, after dressing and discovering what had happened, you went down to the cave. Why?"
"Only two suspects," she explained, "both downstairs."
Batman again nodded, this time approvingly at the girl's deduction. "Nightwing and Robin," he said.
"I didn't-" Dick began to protest.
"I will GET to you..." Batman growled. Dick shut up. "So, you found them down here. How did you identify the guilty one?"
"Gave himself away. 'Wing asked what I did to hair."
"Ran for Redbird."
Everyone looked at Tim, who was red-faced. Batman glanced back to Cassandra and said, "And then you..."
"Hit him in back of head with batarang."
"The black eye?"
"Robin?" Batman asked, seeking confirmation.
"Hnnhtl," Tim grumbled.
"Nightwing?" Batman asked, walking over towards Dick, who was wearing both his costumed and his mask. There were several gouges in the arms of his costume and a small part of the blue on his right arm was darkened with dried blood.
"He started-" Dick began.
Batman didn't wait for his first partner to finish that sentence before interrupting, "Did. Robin. Get. The black eye. From falling?"
"No," Dick answered.
"Then he got it from?"
"Cassandra chasing him up the stairs, tripping him up, and punching him in the face."
Everyone looked at Cassandra, who wasn't red-faced, but was looking a touch embarrassed. Batman said, "And while this was going on, you did what?"
Dick explained, "Once it became clear that Cass was attacking Tim, I yelled at them to stop."
"Threw a bolus at Cassandra."
"And the bolus?" Batman asked, holding up the shredded lines and the three metal balls on the ends of them.
"Mmrphssffnnphr," Dick mumbled.
"The bolus did what?" Batman said, glaring at Dick.
"Wrapped itself around her as she was coming into the cave," Dick explained, pointing to the other woman present.
Batman walked over to Catwoman, who sat unconcernedly polishing her claws, having just cleaned them. He glared down at her.
"What?" Selina said, "He started it."